The invention relates to new metallocene compounds having the racemic structure, which are useful as olefin polymerization catalyst, and their synthetic intermediates.
Metallocene compounds, in which a cyclopentadienyl, indenyl or fluorenyl groups, or derivatives thereof are made ligands, are useful as polymerization catalysts for olefins such as ethylene, propylene or the like under the coexistence of a cocatalyst, for example, aluminoxane. For the preparation for a stereoregular polyolefin have been examined metallocene compounds having various kinds of stereostructures. For a syndiotactic polyolefin preparation is effective ametallocene compound having the Cs symmetry (J. Am. Chem. Soc., 110, 6255 (1988), whereas it is reported that for an isotactic polyolefin preparation is effective a metallocene compound having the racemic structure (Angew. Chem. Int. Ed. Engl., 24, 507 (1985); J. Am. Chem. Soc., 109, 6544 (1987); Chem. Rev., 92, 965 (1992); Organometallics, 13, 954 (1994); Organometallics, 13, 964 (1994)).
Conventionally, the synthesis of a metallocene compound having a racemic structure has been carried out by reacting the dianion produced by the deprotonation of the ligand and metal tetrachloride or its tetrahydrofuran adduct (Scheme 1). ##STR2##
However, since this method gives tarry substances as byproducts, the procedure to separate the aimed metallocene compound having the racemic structure is very tedious (Angew. Chem. Int. Ed. Engl., 24, 507 (1985); J. Organomet. Chem., 288, 63 (1985); Japan Chemical Society ed. Organometallic complex (4th ed. Experimental chemistry series No. 18), Maruzen (1991) p. 81 (in Japanese)), and in many cases a metallocene compound having the meso structure is produced as a byproduct in the nearly same amount as that having the racemic structure, whereby there is such a problem that the separation of the aimed racemic metallocene compound is tedious. Generally, since metallocene compounds having the meso structure decrease the efficiency as a stereoregular polymerization catalyst, they are removed by a combination of purifying operations such as column chromatographic, washing or recrystallizing methods (J. Organomet. Chem., 232, 233 (1982); J. Organomet. Chem., 369, 359 (1989); Chem. Lett., 1853 (1989), Organometallics, 10, 1501 (1991); J. Organomet. Chem., 415, 75 (1991); Organometallics, 13 954 (1994); J. Organomet. Chem., 497, 43 (1995).
Thus, the conventional synthetic methods give a considerable amount of meso metallocene compounds as byproducts, therefore, the yields of racemic metallocene compounds are low, and due to the fact that the procedure in the purification step is tedious, the cost of the synthesis is high, and it is difficult to carry out in an industrial scale.
As a trial for solving such problems is reported the method that after the reaction only the metallocene compounds having the racemic structure are crystallized by appropriately selecting the reaction solvent used(JP, A, 6-122692; U.S. Pat. No. 5,391,790; U.S. Pat. No. 5,616,747). However, in this method the metallocene compound having meso structure is still produced in a nearly half amount, therefore, it can hardly be said that this is an efficient synthetic method.
Further, although the methods by which the metallocene compounds having the meso structure are converted to the metallocene compounds having the racemic structure are studied (J. Organomet. Chem., 342, 21 (1988); Organometallics, 11, 1869 (1992)), pure racemic metallocene compounds cannot be obtained, and furthermore, the decomposition of the metallocene compounds occurs.
On the other hand, the method to selectively synthesize the metallocene compounds having the racemic structure is also reported. In the methods using a ligand in which a bulky substituent is introduced to a cyclopentadienyl skeleton and a ligand having a binaphtyl skeleton in a bridging part, they give low yields and are impractical (Organometallics, 10, 2349 (1991); Organometallics, 10, 2998 (1991)). The method to carry out the reaction at the low reaction temperature of -78.degree. C. is also proposed (JP, A, 1-197490; U.S. Pat. No. 5,103,030), but the yield expected is not obtained. Further, in the synthetic examples of metallocene compounds having the pseudo-racemic structure are used a ligand having the special structure in which 2-position of a indenyl group is bridged by a biaryl group, and the method is practically poor (Organometallics, 12, 2879 (1993); Organometallics, 12, 4391 (1993)). Also, a method employing (CH.sub.3).sub.2 ZrCl.sub.2 has been studied, but the selectivity of the racemic structure amounts at most around 75% in this method. Moreover this might cause trouble in that the reaction tends to take place to predominantly form a meso-type depending on the structure of the ligand (J. Organomet. Chem., 535, 29 (1997)).
On the contrary are reported the methods to obtain the metallocene compounds having the racemic structure in high yields by reacting Zr(NMe.sub.2).sub.4 with a ligand (WO 95/32979; U.S. Pat. No. 5,495,035; Organometallics, 14, 5 (1995); J. Am. Chem. Soc., 118, 8024 (1996)). However, these methods require such a long time as 3-24 hours at the reaction temperature of 80.degree.-160.degree. C., usually 100.degree. C. In the reaction condition, in which heating is required for long time like this, the polymerization or the decomposition of a ligand , which is unstable for heat, occur and it makes the yield low. Additionally, due to the fact that dimethylamine, the starting material of Zr(NMe.sub.2).sub.4, is a gas (b.p. 7.degree. C.) at room temperature, a special reaction equipment corresponding to the gas reaction to prepare Zr(NMe.sub.2).sub.4 is necessary. Further, on the treatment there are various kinds of difficulties such that Zr(NMe.sub.2).sub.4 is very unstable in the presence of air.